1. Field of the Invention
The present invention relates to an image forming apparatus equipped with an image reading device, and more particularly, to an image reading device that includes a pulley unit that supports a driving-force transferring unit for driving a scanning optical system and an image forming apparatus that includes the image reading device.
2. Description of the Related Art
An image reading device, which is generally included in an image forming apparatus such as a copying machine, a facsimile apparatus, or a multifunction product, employs a scanning optical system. The scanning optical system includes a light source, a plurality of mirrors, an imaging lens, and the like.
Generally, the light source and a first mirror are set on a first carriage, while a second mirror and a third mirror are set on a second carriage. Each carriage is configured to linearly move in a sub-scanning direction, pulled by a wire-driven pulley that rotates by a motor as a driving source, a carriage pulley that moves with a drive wire connected to the wire-driven pulley, and a plurality of idler pulleys rotatably arranged.
The idler pulleys are provided at four corners inside of a body of the image reading device and each pair of two idler pulleys extends a drive wire.
The first carriage moves in the longitudinal direction of the image reading device at a predetermined speed V and performs a sub-scanning of the document. The second carriage moves in the same moving direction as the first carriage at a half speed of the first carriage V/2. With this configuration, lights are irradiated from the light source onto a region of the document substantially positioned over the light source, reflected by a first mirror, a second mirror, and a third mirror, and the document is scanned using an imaging lens and a line sensor that performs a main-scanning of the document.
The drive pulley and the idler pulley are mounted at both ends of a side of a body frame in a direction perpendicular to a direction of movement of each carriage (the longitudinal direction). A direction of movement of the drive wire is changed by simultaneously driving each carriage mounted on the two rails (see, for example, Japanese Patent Application Laid-Open No. H11-298653).
FIG. 18 is a schematic for explaining a conventional idler pulley 1. The idler pulley 1 is mounted on a substrate member 3 with a ball bearing 2. The substrate member 3 is fixed to a body 5 of the image reading device using a bolt 4. The ball bearing 2 includes an outer ring member 6 on which the idler pulley 1 is fixed, an inner ring member 8 connected to the outer ring member 6 via a ball 7, and a fixing shaft 9 fitted to the inner ring member 8. When the idler pulley 1 is set on the body 5, the fixing shaft 9 is fixed to the substrate member 3 using, for example, a cashime and the substrate member 3 is fixed to the body 5 using the bolt 4. The drive wire (not shown) is hooked to a dual groove 1a and 1b formed on an outer periphery of the idler pulley 1.
However, when the idler pulley 1 is set in the body 5, the fixing shaft 9 is firstly fixed to the substrate member 3 using the cashime, and the substrate member 3 is further set on the body 5 using the bolt 4. Therefore, number of work units for setting the idler pulley 1 to the body 5 increases. As a result, an operation procedure for setting the idler pulley 1 is troublesome.
In addition, because the inner ring member 8 is provided on the substrate member 3 via the fixing shaft 9 and the ball bearing 2 is unified to the substrate member 3, there are problems that number of components increases and costs for manufacturing the idler pulley 1 increases.
Furthermore, because the idler pulley 1 is provided at each of four corners inside of the body 5, positions for providing the idler pulleys need to be optimized.
Specifically, the idler pulley 1, the fixing shaft 9, and the substrate member 3 are separate components and they need to be put together in the conventional configuration of the pulley unit. If the idler pulley 1 is to be provided at any region of the body 5, the shape of the substrate member 3 needs to be adjusted to the shape of the body 5. Conventionally, the idler pulley 1 is provided on the body 5 with the substrate member 3 optimized to the corresponding shape of the body 5. Namely, the idler pulley 1 with the substrate member 3 in different shapes is provided at each of the four corners inside of the body 5.
Accordingly, precision of providing the idler pulley 1 on the body 5 shows a fluctuation. As a result, it is difficult to run the carriage smoothly and stably using the drive wire.